INTRODUCTION: The treatment and randomization unit in the study will be households located in the areas of the city of Palma (Spain) where individuals must use a personal card to use the bins meant for bio-waste sorting. Hence, each bin use is recorded and associated with one household, allowing us to track the participating households' use of the bio-waste sorting bins.
RECRUITMENT: Participants were recruited first between the 27th of February 2023 and the 30th of June; a second recruitment took place between 30th November 2023 and 25th January 2024. Recruitment was carried out face-to-face by directly approaching people in the street, by the internet through advertisements in social media, and by placing flyers in the city. The participants were informed that the study would be about bio-waste sorting behavior and that they would receive messages by WhatsApp or SMS; in the first round recruitment was facilitated by offering those who signed up to win one of four prizes of €250 each (only one individual per household could sign up). The certified random draw of the winners was performed by the independent firm "Easypromos" on the 27th of July. Each participant signed an informed consent form and answered a questionnaire that collected basic demographic data (number and ages of people in the participant's household, annual income, contact information, …) as well as data on social norms, personal norms, and relationship with nature (beliefs about average environmental sensitivity in the population, motivations to recycle, ...). Among those who signed up, only residents of Palma living in a neighborhood with the new electronic bio-waste sorting bins, in possession of the card required to open the bio-waste sorting bins, and who provided a valid cell phone number were included in the final sample.